Process for the preparation of naphthalene-1 4-dicarboxylic acid

ABSTRACT

NAPHATHALENE-1,4-DICARBOXYLIC ACID IS OBTAINED BY OXIDATION OF 1-METHYL-4-ACETYL-NAPHTHALENE WITH SODIUM DICHROMATE.

United States Patent 3,652,667 PROCESS FOR THE PREPARATION OF NAPHTHA- LENE-1,4-DICARBOXYLIC ACID Hans Frischkorn and Erich Schinzel, Hofheim, Taunus, Germany, assignors to Farbwerke Hoechst Aktiengesell. schaft vormals Meister Lucius & Bruning, Frankfurt am Main, Germany No Drawing. Filed Apr. 2, 1968, Ser. No. 718,240 Int. Cl. C07c 51/28, 63/02 US. Cl. 260-524 M 3 Claims ABSTRACT OF THE DISCLOSURE Naphthalene-1,4-dicarboxylic acid is obtained by oxidation of 1-methyl-4-acety1-naphthalene with sodium d1- chromate.

It is already known from the German Pat. No. 558,471 that naphthalene-1,4-dicarboxylic acid can be obtained by oxidation of 1-methyl-4-acetyl-naphthalene with diluted nitric acid. By this oxidation the naphthalene-1,4-dicarboxylic acid is obtained only in poor yield and low purity. If the same process is carried out with the corresponding 4-benzoyl compound and treatment effected with 20% nitric acid, the benzoyl group remains unchanged and only the formation of 4-benzoyl-l-naphthoic acid takes place. As another method of production the chloromethylation of l-methylnaphthalene and subsequent oxidation with potassium permanganate to form the dicarboxylic acid has been described (Chem. Ber. 84 (1951) p. 636). The total yield of this process, however, amounts only to 16%.

It is also possible to introduce the naphthalene molecule two chloromethyl groups and to oxidize the bis (chloro-methyl)naphthalene obtained with potassium permanganate. Hereby, however, a mixture of 1,4- and 1,5- naphthalene-dicarboxylic acids at a molar proportion of 3:2 is obtained (cf. Chemical Abstracts '55, 23456).

The potassium permanganate-oxidation of 1,4-di-(tert.- pentyl)-naphthalene to give the dicarboxylic acid has also been described (cf. Chemical Abstracts 52, 10025); however, this starting material is only difficultly accessible.

All the oxidation processes with potassium permanganate specified herein have the disadvantage that, besides the side-chains, even the naphthalene nucleus is considerably affected (cf. J. Org. Chem. 30 (1965), 1465). Therefore, isocyclic and heterocyclic compounds carrying oxidizable substituents have been oxidized with dichromate in aqueous phase at elevated temperatures to form the corresponding carboxylic acids by maintaining the ring-system. Thus, alkyl groups of aromatic hydrocarbons can easily be oxidized to carboxylic groups. If, besides alkyl radicals there are even other substituents in the molecule, special methods may be required under certain circumstances, the yield being nevertheless considerably lowered. Thus, for example, o-nitrotoluene cannot be transformed by this method into o-nitro-benzoic acid. The dichromatoxidation process fails "also'with 2-acetylthiophene and other heterocyclic compounds which cannot be oxidized to the corresponding carboxylic acids even under special circumstances.

Surprisingly, it has now been found that 1-methyl-4- acetynaphthalene can be oxidized in very good yield with an excess of alkali dichromate in aqueous solution at temperatures of from 200 to 300 0, preferably from 240 to 260 C., under pressure, into the naphthalene-1,4-dicarboxylic acid.

"ice

The 1-methyl-4-acetyl-naphthalene used as starting substance can be obtained from l-methyl-naphthalene and acetyl chloride according to a Friedel-Crafts process in a yield.

The process according to the present invention may be carried out with sodium or potassium dichromate. It is of advantage to use the sodium compound because of its greater solubility, which may be used in form of an aqueous solution of about 30% strength. The oxidation is advantageously carried through by using sodium dichromate in quantities exceeding the theoretical amount given in the following reaction equation by about 25 to 50%.

2 1/3 m n o ciocn COONa.

+ a 1/3 cr o 2/3 NaOH 1 Na co 2 2/3 H2O COONa.

The pH-value of the solution being of about 4 at the beginning of the oxidation, which corresponds to a concentrated dichromate solution, rises considerably in the course of the oxidation in conformity with the reaction equation above. When using an excess of sodium dichromate the alkali set free during the reaction is buffered off. Below 200 C., no noteworthy oxidation occurs. The reaction starts above a temperature of about 200 C. and is advantageously effected between 240 and 260 C. At this temperature there appears in a closed vessel a vapour pressure of 40 to 45 atmospheres. In order to obtain a good yield, a thorough mixing of the reactants is required.

The naphthalene-1,4-dicarboxylic acid is obtained by the process of the present invention in high purity and almost colourless. It can be used as intermediate in the preparation of dyestuffs, plastics and optical brighteners, especially for those described in US. Pat. No. 3,336,330 and in our copending application Ser. Nos. 613,388 and 655,768.

The following example illustrates the invention but it is not intended to limit it thereto.

EXAMPLE 46 parts by weight of 1-methyl-4-acetyl-naphthalene are heated with a solution of 225 parts by weight of crystallized sodium dichromate (Na Cr O lH O) in 450 parts by volume of water at 250 C. for 18 hours in an autoclave, while stirring vigorously. After cooling, the oxidation solution is filtered off with suction and the residue consisting of chromium(III)oxide washed with water. The filtrate is acidified after being clarified with charcoal with 45 parts by volume of concentrated sulfuric acid, while the precipitated acid is filtered off with suction, freed from sulfate ions by washing and dried. 47 parts by weight (87% of the theory) of the naphthalene-1,4-dicarb0xylic acid having a melting point of from 315 to 320 C. are obtained. As determined by titration with sodium hydroxide solution the acid has a strength of 98.0%.

We claim:

1. A process for the preparation of naphthalene-1,4- dicarboxylic acid which comprises oxidizing 1-methyl-4- acetyl-naphthalene under superatmospheric pressure at about 200 to 300 C. with an aqueous solution contain- 3 4 ing an excess of sodium dichromate thoroughly admixed OTHER REFERENCES therewlth- Fieser et a1.: Organic Chemistry, 3rd ed., 1956, p. 657. 2. The process as clalmed 1n clann 1, Wherem the tem- Friedman et 1 J A Ch m, Soc., May 1965, pp.

perature is about 240 to about 260 C. 1453 7' 3. The process as defined in claim 1, wherein the so- 5 dium dichromate is present in an excess of about 25 to LORRAINE A B R R, Primary Examiner References Cited R. S. WEISSBERG, Asslstant Exammer UNITED STATES PATENTS 10 us. 01. X.R. 2,746,990 5/1956 Fortuin 6t a1. 260524 260523 A 3,439,027 4/1969 Patton et al 260524 

